Diagnostic yield of CBNAAT in the diagnosis of extrapulmonary tuberculosis: A prospective observational study

Background: Extrapulmonary Tuberculosis (EPTB) accounts for 15%-53% of all TB cases. In recent years, cartridge-based nucleic acid amplification test (CBNAAT) has emerged as an important diagnostic tool since the diagnostic yield is higher. We conducted this study to evaluate the diagnostic yield of CBNAAT in EPTB. Methods: One hundred and four patients with EPTB were included in the study. Samples were subjected to CBNAAT, AFB smear, culture for Mycobacterium tuberculosis and histopathology examination (HPE). Yield of each was estimated as compared to a composite reference standard (CRS). Results: The most common EPTB was lymph node TB (48.1%). CBNAAT was positive in 30.76% of EPTB cases. The highest yield was for bone and joint TB (35.7%), followed by lymph node TB (34%) and abdominal TB (33.3%). Taking CRS as the gold standard, sensitivity of CBNAAT was 32.3%, that of AFB culture was 33.3% and that of HPE was 87.2%. Conclusion: When taken as a single diagnostic tool, HPE had highest sensitivity in diagnosing EPTB when compared to CBNAAT and AFB culture. Use of CBNAAT alone for diagnosis of EPTB may result in missing the diagnosis. A combined modality incorporating CBNAAT, histopathology and AFB culture is the best approach for diagnosis of EPTB.